It's a bit complicated, but the general idea is that RTABMAP and other packages are missing because we're using the same subset of packages that ARM devices are using (even though Euclid has an Intel CPU in it).

I've checked with the team, and apparently the decision about which sources are available on the Euclid by default was made in consideration of kernel and support for these sources.

You may add whichever sources you want to your own sources.list , but because not all of those sources can be supported (our kernel is slightly different than linux 16.04), we can't add anything else by default.